AbstractReactions that contribute to denaturation, destruction and quality changes of fish muscle lipids and protein were studied. Compounds with characteristic fluorescence spectra were isolated by extraction and thin layer chromatography from an autoxidizing system consisting of sodium linoleate, Coho salmon myosin and buffer. Similar compounds were also present in extracts from freeze‐dried salmon steaks and salmon kept frozen at −20 C for 1 year. TBA values and oxygen uptake of the autoxidizing system showed initial rapid increases with time followed by a significant decrease in TBA values and gradual leveling off of oxygen uptake upon prolonged oxidation. IR spectra before and after borohydride reduction and UV, visible and fluorescence spectra indicated the presence of C=N functional groups in extracts from the various samples. These compounds were not extractable from the control myosin solutions allowed to oxidize without addition of linoleate. Amino acid analyses of the myosin from the autoxidizing system, when compared with nonoxidized myosin‐linoleate systems, indicated significant decreases in the amounts of histidine, lysine and methionine following oxidation. These reactions apparently contribute to the denaturation and destruction of the lipids and protein in the model system, as well as in a frozen or freeze‐dried product.